This invention relates to a cleaning system for the impression cylinder of offset sheet-fed printing presses.
There has been continual development of blanket cylinder cleaning systems for offset printing presses and many systems for practical use have been proposed. As shown in FIG. 11, the impression cylinder 1 of the offset sheet-fed printing press, has a finger mechanism mounting space 1a in which is mounted a finger shaft 2 to which is mounted a finger 3, provided so that it protrudes from the surface of the impression cylinder. Because of this, even when cleaning is performed for the dirt, paper dust or the like by wiping the impression cylinder between a magazine roll and a take-up roll, the finger 3 becomes an obstruction to make automatic cleaning of the impression cylinder difficult to the extent that it has to be performed manually.
Also there is limited space around the impression cylinder and not only does such cleaning have to be made in an awkward posture, it is also dangerous as it is necessary to clean the impression cylinder while rotating it at a low speed. Moreover, the dirt stuck to the cylinder is difficult to clean off in itself and the time required for cleaning reduces the production efficiency of the printing press.
To counter this problem, cleaning systems such as the one disclosed in Japanese Patent Application Number 92456/1988 have been proposed. As shown in the sectional view in FIG. 10, indicating the status of contact between the cleaning system and the impression cylinder, the magazine roll 5 and the take-up roll 6 of the cleaning cloth 4 have the same configuration as a conventional system but the line pressure contact device is a support plate 7 that has the shape of an inverted letter V, and a blade 8 mounted to one of its ends. The cleaning cloth 4 fed out from the magazine roll 5 is pressed by this plate in a line against the impression cylinder 1, and the other end of the support plate 7 forms a guide portion 9 provided on the side of the take-up roll 6 to form a configuration whereby the cleaning cloth 4 pressed by the blade 8 to form a line against the impression cylinder 1, is guided and pressed along an arcuate circumferential surface of the impression cylinder 1 so that there is an area of contact in the form of an arcuate circumferential surface, and is then taken-up by the take-up roll 6. This is to say that the system comprises a cleaning cloth 4 to directly remove the dirt on the impression cylinder 1, a magazine roll 5 to progressively reel-out the cleaning cloth 4; a take-up roll 6 to hold and take-up the cleaning cloth 4; a blade 8 to press the cleaning cloth 4 against the impression cylinder 1, a nozzle 12 provided on the cleaning liquid supply pipe 11 and forming means to dampen the cleaning cloth 4; an inverted-V shaped support plate 7 provided with a guide portion 9 for supporting the blade 8 and the cleaning liquid supply pipe 11 and also for holding the cleaning cloth 4 on the take-up side against the surface of the impression cylinder; and a frame 13 for supporting the inverted-V shaped support plate 7 provided with a guide portion 9 holding the cleaning cloth 4 on the take-up roll side, in contact with the impression cylinder 1, and also provided with a finger 3 mounted to the finger shaft 2 inside the finger mechanism mounting space 1a of the impression cylinder 1. The finger shaft 2 is provided with a finger escape cam 14. In addition, the cleaning system is provided with an air cylinder as a movement system for the purposes of advancing and retreating the cleaning system to and from the impression cylinder so that contact with the impression cylinder is prevented when the impression cylinder is rotating at a high speed, and a one-way clutch and air cylinder for progressively moving the cleaning cloth and taking it up. Movement of the blade 8 to move the cleaning cloth 4 with respect to the impression cylinder 1 is performed by a suitable means. Moreover, as shown in FIG. 10, reference numeral 15 indicates a rotating support shaft 15 for bringing the frame 13 into and out of contact with respect to the impression cylinder 1. In addition, a mechanism that uses the action of a cam or the like to rotate the frame 13 around the center of a rotating support shaft 15 can be provided instead of an escape cam so that the cleaning cloth 4 does not come into contact with the finger 3.
However, in a cleaning system as disclosed in Japanese Patent Application Number 92456/1988 as described above, the cleaning of the impression cylinder is performed by a blade pressing the cleaning cloth against the surface of the impression cylinder so that the portion of the cleaning cloth in contact forms an arcuate circumferential surface around a portion of arcuate circumferential surface of the impression cylinder. Thus, is possible for dirt to be cleaned away by the blade for the portion close to the finger 3 but the remainder of the arcuate circumferential surface of contact has a small pressure force and there is a poor transfer of dirt to the cloth. Therefore, the full cleaning performance of the cloth is not displayed, and dirt may remain on the impression cylinder. Also, in order to make the pressing force of the blade uniform, it is necessary to increase the precision of contact along the full length of the blade. However, a sufficient precision cannot be obtained with the cleaning apparatus described above, and the result is that the cleaning performed by the blade is not uniform.